1. Field of the Invention
The present invention relates to a method for preparing a semi-furanic copolyamide containing at least one furanic dicarboxylic acid moiety and at least one aliphatic diamine moiety in the backbone using solid-state polymerization. More particularly, the present invention relates to a method for preparing a semi-furanic copolyamide that uses a biomass-derived furanic dicarboxylic acid as a raw material.
2. Description of the Related Art
With the recent violently fluctuating oil prices and increasing concern about environmental pollution, there has been a growing interest in the development of natural polymers found in nature and bioplastics as synthetic polymers synthesized from biomass-derived monomers due to their potential replacements for existing fossil fuels.
The world's annual biomass production is estimated to be 10 times the world's total annual energy consumption. The idea to effectively use biomass as a renewable energy source is on the rise. Thus, strategies to use biomass have recently been issued in the field of biotechnology. Biodegradable plastics have been suggested as examples of the strategies. Particularly, bioplastics are recyclable materials that are produced using biomass resources as raw materials by biological or chemical processes, but they have the problem of high production costs and are required to have high performance.
Much research has been conducted for many years on natural polymers, such as natural rubbers and celluloses. Such natural polymers have already been used in large amounts. The history of research on synthetic polymers derived from biomass is not relatively long. Only a few of the synthetic polymers are commercially successful and are applied to practical use.
The most well-known synthetic polymers are polylactides, which are currently produced on an industrial scale. Research is underway to improve the physical properties of polylactides in countries around the world. In addition to this research, studies are underway to synthesize polyolefins using monomers converted from bioethanol and to synthesize triglycerides as major ingredients of animal and vegetable oils and fats. Most monomers for polyamides, such as adipic acid and caprolactam, are currently produced by petrochemical processes. Proposals have been made recently on methods for producing the monomers from biomass. However, studies on the synthesis of polyamides based on the proposed methods still remain at the early stages because the methods are disadvantageous in terms of economic efficiency compared to petrochemical processes. Examples of polyamides synthesized using biomass-derived monomers include polyamide 11 produced from castor oil and polyamide 4 produced from glucose.
Melt polymerization, solution polymerization, and solid-state polymerization are known as processes for producing the polyamides.
Melt polymerization is advantageous in that a polymer can be produced in a single step. However, when it is intended to produce a polymer having a high melting point by melt polymerization, the polymer is likely to undergo thermal decomposition, gelation, and other troubles, resulting in deterioration of quality. As the polymerization proceeds, the polymer becomes viscous, which makes stirring and temperature control difficult. Further, by-products are not easy to remove. As a result, it is difficult to obtain a high molecular weight of the polymer. For solution polymerization, only a limited number of solvents, such as concentrated sulfuric acid, can be used to dissolve polyamides. That is, the choice of solvents is restrictive in solution polymerization.
Solid-state polymerization for the production of a polymer is performed at a temperature between the glass transition temperature and melting point of the polymer. This reaction temperature can reduce the possibility of heat-induced side reactions. Solid-state polymerization is performed in the absence of solvents. Accordingly, solid-state polymerization is free from disadvantages associated with the use of solvents, unlike solution polymerization. Solid-state polymerization for the production of a polymer is generally performed by the following procedure. First, a prepolymer having a low molecular weight is produced by melt polymerization. The prepolymer is pulverized into a powder, and then the prepolymer powder is introduced into a suitable reactor, such as a packed bed reactor, a fluidized bed reactor, a fixed bed reactor or a moving bed reactor. The prepolymer is polymerized in a solid state at a temperature between the glass transition temperature and melting point of the polymer while feeding a continuous flow of a sweep fluid for removal of by-products into the reactor. The polymerization increases the molecular weight of the prepolymer.
The presence of an aromatic monomer in a polyamide increases the crystallinity of the polyamide and ensures superior heat resistance, stiffness and dimensional stability of the polyamide. Due to these advantages, polyamides can be used as engineering plastics in a wide range of applications where high strength and good heat resistance are required, particularly, electronic/electrical materials, such as surface mounting devices (SMTs), LED reflectors and I/O connectors, lightweight interior/exterior materials for automotive vehicles capable of substituting for metals to reduce the weight of automotive vehicles and protect automotive vehicles from corrosion, industrial materials, and aeronautical materials, which are usually produced by injection molding. Examples of such semi-aromatic polyamides include polyamide 4,T produced from terephthalic acid and 1,4-butanediamine, and polyamide 6,T produced from terephthalic acid and hexamethylenediamine.
Polyamide 4,T and polyamide 6,T have high crystallinity and superior heat resistance but are not suitable for injection molding due to their higher melting temperatures, 430° C. and 370° C., respectively, than those of conventional polyamides. Accordingly, it is difficult to use the polyamides in the above-described applications. Thus, attempts have been made to produce highly heat resistant copolyamides suitable for injection molding by adjusting the melting points of polyamide 4,T and polyamide 6,T within the range of 300 to 330° C. As the copolyamides, copolyamide 4,T/4,6, copolyamide 6,T/4,6, and copolyamide 4,T/6,T/4,6 have been proposed. Copolyamide 4,T/4,6 is obtained by copolymerization of polyamide 4,6 produced from adipic acid and 1,4-butanediamine and polyamide 4,T. Copolyamide 6,T/4,6 is obtained by copolymerization of polyamide 4,6 and polyamide 6,T. Copolyamide 4,T/6,T/4,6 is obtained by copolymerization of polyamide 4,6, copolyamide 4,T and polyamide 6,T.
Efforts have been made to produce semi-furanic copolyamides as substitutes for semi-aromatic copolyamides by introducing FDCA instead of terephthalic acid. However, the colors of the semi-furanic copolyamides tend to change or the molecular weights of the semi-furanic copolyamides are not sufficiently high. Due to these problems, none of the semi-furanic copolyamides reported hitherto are successful. Under such circumstances, there is a need for a novel semi-furanic copolyamide and a preparation method thereof.